RAW headroom

Raw files have an inherently wider dynamic range than JPEGs, because the date that they contain has a greater bit depth. What this means in practice is that careful processing of a raw file will reveal a lot more tonal information in the brightest and darkest areas of a scene than an equivalent JPEG. This allows you to rescue poor exposures more effectively, and - should you want to - you can also combine different versions of the same raw file to create composite images with a broad tonal range. Making extreme brightness adjustments to JPEGs is generally a bad idea, since it compresses the number of tones in the image (which is less than a raw file in the first place) and can lead to banding and false colors.

Experience has told us that there is typically around 1 EV (one stop) of extra information available at the highlight end in RAW files and that a negative digital exposure compensation when converting such files can recover detail lost to over-exposure. As with previous reviews we settled on Adobe Camera RAW for conversion to retrieve the maximum dynamic range from our test shots. Raw files were 14-bit NEF, shot in lossless (uncompressed) mode for maximum quality.

As you can see the default Adobe Camera RAW conversion delivers less dynamic range than JPEG from the camera (a more contrasty tone curve and less noise reduction in shadows). It's possible to get considerably more than this out of the file, (for example, our ACR 'Best' parameters) but pushing the tone curve this much results in a very flat image that in a 'real world' scene would look entirely unrealistic. The important point to remember though is that even though you don't necessarily want to go to these extremes, there is a lot more leeway for tonal adjustments in the D3S's raw files than from its JPEG output, as we can see from the following 'real world' examples.

To test how much exposure latitude the raw file actually gives in everyday shooting, we selected two images that show highlight clipping at their 'correct' metered exposure. The first image is a general daylight scene containing a range of tones, and the other is a very tricky scene, containing strong backlighting. In both instances, we wanted to see how much more latitude for adjustment we have with the raw files (which were converted using Adobe's D3S-specific profile) compared to their equivalent JPEGS.

JPEG (metered exposure)

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RAW (-1EV exp. adjustment applied in ACR)

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RAW (-2EV exp. adjustment applied in ACR)

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Here, the camera has delivered a bright, pleasant exposure which has rendered the majority of the scene accurately. However, a small area of the rider's face, neck and shoulder is clipped, and shows virtually no detail in the JPEG image. We can clearly see, however, that plenty of detail and accurate tonal information can be recovered from the simultaneously captured raw file. The image as a whole is too dark as a result of our -2EV adjustment, but this raw file is an ideal candidate for selective exposure adjustment using layer masking etc.

JPEG (metered exposure)

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JPEG (-2EV exp. adjustment applied in ACR)

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RAW (-2EV Exposure adjustment applied)

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This image provides a salient example of why we would recommend shooting in raw capture mode when capturing scenes under tricky lighting. This scene would actually be an ideal candidate for Nikon's Active D-Lighting function, but the original JPEG/Raw pair was shot with the function disabled. So here, we wanted to see how much of the bright sky we could 'bring back', post-capture.

Notice how badly the JPEG reacts to being darkened. The delicate peach hues of this area of sky in the original exposure have turned a urinous yellow, and banding can be seen where the file simply doesn't contain enough colors to render this subtle color transition accurately. The 14-bit (uncompressed) Raw file, on the other hand, can be darkened by the equivalent of -2EV in Adobe CameraRAW without any obvious penalties in color rendition in this area, and without any banding that we can see in the JPEG file.

Working on this sort of scene is where the extra bit-depth of the D3S's raw files really comes in handy, and both of the examples we've shown here suggest that raw files contain at least 1EV of extra information in highlight areas compared to equivalent JPEGs.